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Gametogenesis of the Gall-Fly, Neuroterus lenticularis.—Part II. 
By LeonarD Doncaster, M.A., Fellow of King’s College, Cambridge. 
(Communicated by Prof. W. Bateson, F.R.S. Received January 25,— 
Read March 16, 1911.) 
[PLate 17.] 
Introduction. 
In the first part of this paper* I described the life-history, spermato- 
genesis, maturation of the fertilised egg, fertilisation and segmentation 
divisions of the summer generation of the gall-fly Newroterus lenticularis 
(Spathegaster baccarum), and gave some observations on the maturation of 
the eggs of the spring generation, and on the somatic mitoses in males and 
females. These latter observations were admittedly incomplete owing to 
lack of material, and this second part of the paper attempts to complete 
the account of what was left uncertain in the first communication. Before 
proceeding to describe my fresh observations it may be well shortly to 
summarise the results arrived at in the first part. 
The spring generation of IV. lenticularis consists of females which lay 
parthenogenetic eggs; those laid by some females develop into males, those 
laid by others develop into sexual females, both of which hatch in June. 
The eggs of the summer females undergo a double maturation division, 
leaving 10 chromosomes in the nucleus of the mature egg. The sperma- 
togonia of the males in the same generation have 10 chromosomes; the 
first spermatocyte division is suppressed ; in the second spermatocyte 
division the chromosomes divide, 10 entering each spermatid. A small 
staining extra-nuclear body found in the spermatocytes does not divide, and 
is included in only half of the spermatids. In fertilisation, the egg and 
sperm nuclei each contain 10 chromosomes, and the segmentation divisions 
of the fertilised egg show 20. For a complete study of the maturation and 
segmentation of the parthenogenetic spring eggs my material was 
insufficient, but it suggested that the eggs laid by some females underwent 
maturation and showed 10 chromosomes in the segmentation divisions, and 
that others had no polar divisions and showed 20. Since somatic and 
cogonial mitoses of the summer female have 20 chromosomes, but the 
spermatogonial mitoses and those of the developing nervous system in the 
male only 10, it was suggested that the eggs which undergo maturation 
* “Roy. Soc. Proc.,’ B, vol. 82, p. 88. 
